Example Journeys and Cost , I will be using the cheapest services of each carrier

15K 3 Hours ( Around Town )

CarNext Door : 15$ Time+5$ Mile+ 5$ Booking = 25$

Flexicar : $40.5 Time = 40.5$

50k 1 day ( Around City )

CarNext Door : 25$ Hour + 5$ Booking + 16.5 Milage = 46.5$

Flexicar : $79 Day Charge = 79$

3 day 400k ( Weekend Trip )

CarNext Door : 132$ Milage + 5$ booking + 75$ Time = $212

Flexicar : 237$ Time + 39$ Mileage = $276

Conclusion

Car Next Door is still the cheapest providing you can find one of their cars for 5$/Hour ( 25$ per Day). Car Next door does have a higher insurance excess of 2000$ compared to 1200$ from Flexicar ( both can be brought down with extra money ) however Flexicar has a 49$ Annual fee